This invention relates to improvements in hydraulic feed systems for rotary drills. More particularly it is concerned with providing an improved and economically advantageous system for rapidly advancing and retracting the rotary head of a conventional rotary rock drill.
Conventional rotary drills in attempting to obtain rapid speed or retract operations increase the pumping capacity of their systems. This arrangement may have an advantage during a portion of the drilling cycle, but can be a detriment at other times; such as, when penetrating hard rock at a relatively slow rate, the excess energy used develops into heat which may be destructive of the hydraulic system.
The system of the present invention is designed to use only the energy required to fulfill the need at a given time.
Accordingly, a feature of the system of the present invention lies in the employment of a pressure compensating type hydraulic pump which functions to feed only the oil required for the drill head to penetrate a given strata at up to the maximum feed rate of the system, all at the driller's predetermined feed pressure. The predetermined feed pressure would be that most economical for the bit size being used.
Another feature of the system lies in the employment of a pilot operated dump valve which will relieve the pulldown/hoist cylinders return oil at the time the cylinders are retracting and the rotary head is in the hoisting mode. The dump valve is arranged to relieve the return oil direct to sump, thereby avoiding the usual return route and associated back pressures. This feature is especially advantageous during a rapid retract mode of retraction since in this mode the system oil is greatly increased by adding to it the rotation system oil flow.
A further feature of the feed system is a pilot operated high capacity directional valve arranged to be actuated by a signal induced only when the oil of the rotation oil system is added to the feed system.
Another feature of the invention lies in the organized arrangement of elements in the hydraulic feed system whereby the latter is selectively operable in various modes; namely, standard feed; regeneration feed; standard retract; and rapid retract.
Various advantages attributable to the system are increased feed and retract speeds that considerably reduce drilling time; capacity of the drill bit to penetrate the strata at maximum speed; materially reduced heat build up and back pressure as a result of routing return oil flow directly to sump at minimum pressure; reduction in wasted horsepower by using pressure compensating and variable volume pumps that work only when required; and accordingly a relatively economical system.